1. Field of the Invention
The present invention relates to a secondary battery, and more particularly to a secondary battery pack including a bare cell having an electrode assembly, a can and a cap assembly and a protective circuit module electrically connected to the bare cell by applying molding resin thereto.
2. Description of the Related Art
Secondary batteries are rechargeable batteries, which can be made in a compact size with a large capacity. Due to these characteristics of the secondary batteries, studies and research have been carried out for developing secondary batteries. Among secondary batteries, Nickel Metal Hydride (Ni-MH) batteries, Lithium (Li) batteries and Lithium-Ion (Li-ion) batteries have been developed and used recently.
Generally, a bare cell of a secondary battery can be made by accommodating an electrode assembly having an anode, a cathode and a separator in a can made from aluminum or an aluminum alloy, sealing the can by using a cap assembly, and injecting an electrolyte into the can. Although it is possible to make the can using an iron material, the can may also be made using aluminum or an aluminum alloy because aluminum or the aluminum alloy allows the secondary battery to be lightweight without causing the can to erode even if the secondary battery is used for a long period of time under high voltage.
The sealed bare cell is connected to safety units, such as a positive temperature coefficient (PTC) device, a thermal fuse and a protective circuit module (PCM) or battery components, and is accommodated in a separate pack. Otherwise, when the bare cell is connected to the PCM and battery components, molding resin is filled in a gap formed between the bare cell and the PCM or battery components so that the bare cell is integrally formed with the PCM and battery components, thereby forming a battery pack.
The safety units are connected to a positive terminal and a negative terminal of the bare cell by means of a conductive structure called a “lead plate”. When voltage of the battery suddenly rises due to high temperature of the battery or an excessive recharge/discharge of the battery, the safety units shuts off current to the battery, thereby preventing the battery from being damaged.
FIG. 1 is a schematic exploded perspective view showing a conventional lithium ion battery pack before molding resin is applied thereto, and FIG. 2 is a perspective view showing a conventional lithium ion battery pack assembled by means of molding resin.
Referring to FIGS. 1 and 2, a protective circuit module 30 is aligned in parallel to one surface of a bare cell 10 of the lithium ion battery pack in which positive and negative terminals 11, 12 are formed. In addition, molding resin is filled in a gap formed between the bare cell 10 and the protective circuit module 30. Although molding resin can be applied to an outer surface of the protective circuit module 30 when filling molding resin in the gap, external input/output terminals 31, 32 of the battery must be exposed to an exterior.
The positive terminal 11 and the negative terminal 12 are aligned on one surface of the bare cell 10 in parallel to the protective circuit module 30. The positive terminal 11 can be formed as a part of a cap plate 13 made from aluminum or an aluminum alloy, or can be formed as a metal plate containing nickel coupled to the cap plate 13. The negative terminal 12 protrudes from the cap plate 13 and is electrically insulated from the cap plate 13 by means of an insulation gasket aligned around the negative terminal 12.
The protective circuit module 30 includes a panel made from resin and circuits formed on the panel. The external input/output terminals 31, 32 are formed at the outer surface of the protective circuit module 30. The protective circuit module 30 has a shape and a size identical to those of a corresponding surface of the bare cell 10, in which the cap plate 13 is formed.
The protective circuit module 30 is provided at an inner surface thereof with a circuit section 35 and connection terminals 36, 37. The circuit section 35 includes protective circuits for protecting the battery from being over-charged or over-discharged. The circuit section 35 is electrically connected to the external input/output terminals 31, 32 by means of a conductive structure extending by passing through the protective circuit module 30.
Connection leads 41, 42 and an insulation plate 43 are aligned between the bare cell 10 and the protective circuit module 30. The connection leads 41, 42 are generally made from nickel and electrically connected to the cap plate 13 and the connection terminals 36, 37 of the protective circuit module 30. The connection leads 41, 42 have L-shaped or planar-shaped structures. In addition, the connection leads 41, 42 can be connected to terminals 11, 12, 36, 37 by means of resistance spot welding. In FIGS. 1 and 2, a breaker is additionally provided on the connection lead 42 provided between the protective circuit module and the negative terminal. In this case, the breaker is not formed on the circuit section 35 of the protective circuit module. The insulation plate 43 is provided in order to insulate between the connection lead 42 connected to the negative terminal 12 and the cap plate which functions as an anode.
However, when a battery pack 1 is made by assembling the bare cell 10 with the protective circuit module 30 and battery components using molding resin, a molding resin section 20 for fixedly coupling the protective circuit module 30 and battery components to the bare cell 10 may be easily twisted or bent if external force is applied thereto because the molding resin section 20, which is made from a soft material different from the bare cell 10 including the cap plate 13 and the can made from a metal, only makes contact with a small portion of the bare cell 10.
FIG. 3 is a perspective view showing the molding section 20 twisted from the bare cell due to external force applied to a conventional battery pack.
Referring to FIGS. 1 to 3, if the molding section 20 is twisted from the bare cell 10 more than a predetermined angle, a problem may occur in an electric connection line formed through the positive and negative terminals 11, 12 of the bare cell 10. The connection leads 41, 42, and the input/output terminals 31, 32 of the protective circuit board 30 and safety units of the battery may become non-operational, even if the molding resin section 20 is not completely broken.
In relation to a twist of the battery pack caused by external force applied to the battery pack in a direction indicated by arrows in FIG. 3, if the connection leads 41, 42 have planar structures, the conventional battery pack has no protrusions protruding vertically to a cap plate surface in order to prevent the battery pack from being deformed when the molding resin section 20 is twisted or slidably moved with respect to the bare cell 10. In addition, even if the connection leads 41, 42 and the connection terminals 36, 37 have L-shaped structures so that welding parts of the connection leads 41, 42 and the connection terminals 36, 37 may protrude from the cap plate surface, since the welding parts protruding from the cap plate surface are not provided for reinforcing mechanical strength of the battery pack, but rather are provided for an electric connection on a predetermined part of the cap plate surface only, the welding parts cannot function as supporters against external force causing the battery pack to twist or bend.